Maggie. I'm Karen, currently also pregnant with number 2 (Due in Feb).
In my area there isn't usually a routine appointment between 16 and 24 weeks anyway (probably because the 20 week scan takes its place). I would ask about your scan date if possible. I knew the date of mine several weeks in advance.
If they still don't want to see you more often after 25 weeks then I would definitely question it. Blood pressure etc. aren't usually a problem early on, but should be checked regulary in the third trimester. In the meantime if you need to see a midwife for any reason then just book an appointment anyway.